In high frequency systems, it is common to employ waveguides to guide electromagnetic waves or sound with minimal loss of energy by restricting expansion of the electromagnetic waves propagating within the waveguides to one or two dimensions. Depending on the nature of the electromagnetic waves to be propagated, the waveguides may take different forms. Also, in many instances, filters are employed to allow electromagnetic waves at some frequencies to pass and travel along the waveguides, while rejecting electromagnetic waves at other frequencies. For example, when propagating radio frequency (RF) waves, hollow, open-ended, conductive metal waveguides are often employed. In some instances to provide the desired filtering, these hollow metal waveguides are fitted with a solid insert formed of high dielectric constant material.
Waveguides such as those described above have been employed in thermoacoustic imaging systems. Thermoacoustic imaging is an imaging modality that provides information relating to the thermoelastic properties of tissue. Thermoacoustic imaging uses short pulses of electromagnetic energy, such as RF pulses, directed into a subject to heat absorbing features within the subject rapidly, which in turn induces acoustic pressure waves that are detected using acoustic receivers such as one or more thermoacoustic or ultrasound transducer arrays. The detected acoustic pressure waves are analyzed through signal processing, and processed for presentation as thermoacoustic images that can be interpreted by an operator.
In order to direct RF pulses into the subject during thermoacoustic imaging, a radio frequency (RF) applicator employing a waveguide is coupled to tissue adjacent a region of interest (ROI) within the subject to be imaged. Sub-optimal coupling of the RF applicator to the tissue may cause issues such as inefficient energy transfer, reduced heating rates, reduced signal intensity, non-uniform energy deposition, tissue hotspots, tissue overheating, RF power supply damage, and poor image quality. Factors that lead to sub-optimal coupling of the RF applicator to the tissue include variability in the size of the subject, the size of tissue within the subject, the geometry of tissue within the subject, the composition of tissue within the subject, etc.
During fabrication of waveguides fitted with solid inserts, air gaps can form between the facing surfaces of the waveguides and the solid inserts. Unfortunately, the air gaps can change the frequency characteristics of the waveguides in an unpredictable manner. As will be appreciated, improvements are therefore desired. It is therefore an object at least to provide a novel radio frequency (RF) applicator and a thermoacoustic imaging system employing the same and a novel method of assembling a radio frequency applicator.